Numerous means have been sought to improve the fuel-efficiency of moving bodies, and especially moving bluff bodies, by reducing their aerodynamic drag. In the field of surface transportation, and particularly in the long-haul trucking industry, even small improvements in fuel efficiency can reduce annual operating costs significantly. It is therefore advantageous in the design of a vehicle to reduce drag forces, thereby increasing the aerodynamic properties and efficiency of the vehicle.
The over-the-highway cargo hauling tractor-trailer combination is one vehicle that experiences excessive aerodynamic drag. Generally described, tractor-trailer combinations typically include a tractor having a so-called fifth wheel by which a box-like semi-trailer may be articulatedly attached to the tractor for transportation of the semi-trailer. By providing the articulated connection via the fifth wheel, a space or gap is formed between the aft facing rear wall of the tractor cab and the forward facing front wall of the semi-trailer. It is well known that this gap, or the gap between succeeding trailers (not shown) of a tractor trailer combination causes wake regions and, as a result, aerodynamic drag.
Previous investigations of aerodynamic drag of tractor-trailer combinations resulted in widespread adoption of fixed air deflectors mounted on the roofs of tractor cabs and/or trailer bodies, and wholly redesigned tractors that utilize aerodynamic fairings to gradually increase the relatively small frontal area of the tractors to match, and to blend smoothly with, the larger cross-section of typical trailers, in an attempt to deflect air efficiently across the gap between cab assemblies and trailer bodies. Current fixed air deflectors and fairings help guide frontal airstreams around the front of tractor-trailer combinations and/or smooth the air flow over the gap between the articulated bodies, thereby reducing aerodynamic drag and improving fuel efficiency.
While in some instances these systems reduce the effective gap between bodies, such gap reduction is incidental, often resulting in a significant amount of drag caused by the gap. Thus, aerodynamic drag reduction across the air gap between adjacent articulated tractor-trailer combination bodies is only partially achieved by fixed fairings and deflectors. Additionally, these roof mounted air deflectors and tractor fairings may help to reduce the aerodynamic drag in zero cross wind flow conditions, but these devices do not provide significant drag reduction when crosswind flow is present.